I do see that I misread your statement. I apologize. You said "She publicly shamed the wrong guy!" That does mean that you think public shaming can be appropriate, if applied to the right person.
I still think arguments which use the term "public shaming" are uselessly vague. If you mean defamation, then just say defamation.
Defamation has a reasonably well-defined meaning in law and ethics, though the details vary widely depending on the jurisdiction. As this took place in the US, I do not see how there's a valid legal claim for defamation under US/California law.
I suspect though that you're talking about morals and ethics, and not just the law. The neat thing I've learned about the law is that it provides useful insights for how at least judges think about the ethics and morality behind the law, and those views can help understand the issue.
For example, SMITH v. MALDONADO is a California court case which addressed "Can a defamatory innuendo be created by the act of "highlighting" or visibly emphasizing certain selected passages in a concededly truthful and accurate newspaper article? May an action for defamation lie against persons who copy and disseminate such a truthful newspaper article, after having themselves highlighted one portion of the article that mentions other individuals in a context or manner that inferentially associates those individuals with alleged criminal activity? The issue is apparently one of first impression."
I think the concept of "first impression" is quite appropriate to this context, even if the details are different. The court decided that "first impression" could not be used as the basis for defamation, saying:
"Any other result would have a deleterious impact on all forms of written and oral speech. If we were to accept appellants' contention, the unavoidable effect would be to discourage the dissemination of accurate news reports. This result would raise obvious First Amendment concerns. We need not confine our consideration to the republication of newspaper articles, moreover. Writers and public speakers in general would have to take care they did not place the "wrong" emphasis on truthful, accurate statements of fact. The resulting chilling effect on the free flow of ideas and information would be substantial."
"Moreover, if a plaintiff could plead defamation based on an alleged innuendo derived solely from highlighting a true statement of fact, the door would be open to all kinds of subjective considerations of what does or does not constitute undue emphasis. Thus, in any defamation case the court would be forced to consider the particular type of emphasis used, and its effect on the person or persons to whom the material was published. Courts in libel cases would have to consider the distinctive effects of underlining, italicization, typeface, and the size, style or color of print used; courts in slander cases would be compelled to analyze the effects of variations in vocal tone, inflection, timbre, volume and pitch. If highlighting or emphasis alone could be found to create a defamatory innuendo as a matter of law, courts would also have to analyze the subjective intent of the person doing the highlighting. Otherwise, the highlighter could be liable if a person to whom the highlighted material was published misinterpreted it by giving the highlighting a falsely defamatory meaning, even if the highlighter had no such defamatory intent. What was he or she trying to communicate by highlighting or emphasizing and then publishing the material? If the added emphasis simply communicates "importance," how or why was the emphasized material "important"? The substantive and procedural difficulties posed to courts and litigants by such subjective analysis would be daunting. Even without considering the manifest constitutional ramifications of expanding the tort of defamation to include emphasis or highlighting of otherwise truthful material, strong considerations of public policy would preclude such an outcome."
While that case was about someone redistributing text from a newspaper, with parts they highlighted themselves, I think you can see how the underlying concept of "first impression" applies to image composition of a tweet.
I agree with the court's view here. If this incident is viewed as "defamation", then "the door would be open to all kinds of subjective considerations of what does or does not constitute undue emphasis." Which is exactly what's happened. And that's why the discussions have gone nowhere.
Morally and ethically speaking, I believe that saying this photograph+text is defamation is a bad idea, as doing so puts a "substantial" "chilling effect on the free flow of ideas and information".